Quasi-analog reconstructions of original amplitude and frequency varying analog signals have been provided heretofore in communication systems by sampling, quantizing and encoding an audio input signal into digital signals and using the binary bits of the digital signal of each sampling period to switch discrete voltages supplied from respective power sources into or out of a series voltage summation output line. The output voltages thus produced in successive sampling periods provide the desired quasi-analog reconstruction of the audio input signal.
One such known communication system is the subject of U.S. Pat. No. 3,305,855 issued Feb. 21, 1967 to Hisashi Kaneko. In that system, 2.sup.N standard power sources are logically switchably controlled during each sampling period in response to an N-bit codeword, the power sources supplying non-linearly related voltages.
Techniques for switchably interconnecting a plurality of discrete power supplies in series for the purpose of providing predetermined increments in kilovolt power have, moreover, been disclosed in U.S. Pat. No. 3,723,855 issued Mar. 27, 1973 to P. Schuleshke. In addition, a transformer device for converting digital information into a precisely controlled analog voltage, wherein various taps on an autotransformer are configured to provide binary related analog voltages and wherein such voltages are serially combined in response to ten-bit binary control signals, has been disclosed in U.S. Pat. No. 3,603,971 issued Sept. 7, 1971 to W. Woschetsky et al.
Still further, there is a large body of prior art wherein resistive ladder-like networks are switched under control of digital input signals to provide analog output voltages and wherein, for the most part, only one power source is used and the resistive ladders produce stepped voltages which are subsequently logically combined. Illustrative of this body of prior art are: U.S. Pat. No. 4,160,244 issued July 5, 1979 to J. E. Solomon et al; U.S. Pat. No. 3,877,021 issued Apr. 8, 1975 to J. Raamot; and U.S. Pat. No. 3,044,007 issued July 10, 1962 to R. C. Akers.